1. Field of the Invention
The present invention relates to multi-layer capacitor structures. More specifically, the invention relates to a novel multi-terminal capacitor structure.
2. Description of the Related Art
As the speed at which integrated circuits are operated increases, the generation of associated switching noise increases. Switching noise, however, can have a very detrimental effect on the performance of integrated circuits. Digital integrated circuits require both stable voltage references and uniform power distribution among all integrated logic devices for signal definition. Moreover, in mixed systems having both analog and digital circuits, the switching noise generated by the digital circuits can also have a detrimental effect on the analog circuits. In many instances, reducing the effects of the digital circuits on the analog circuits in a mixed system is a very challenging problem for system designers.
Discrete capacitors are commonly used for local power supply decoupling of integrated circuits to reduce the effects of switching noise. But, current capacitive methods and structures may be inadequate for reducing noise on integrated circuits, especially at higher frequencies of operation.
A known technique for reducing switching noise is to utilize decoupling capacitors between associated voltage pins. It is known that switching noise of a circuit can be reduced by minimizing the inductance while maximizing the capacitance of an electrical path that exists between the power and ground terminals. Discrete capacitors are typically used as decoupling capacitors.
The use of discrete capacitors has a number of inherent limitations. Discrete capacitors are two-terminal devices which unavoidably use extrinsic leads. The resistance and inductance of these leads place a lower bound on the capacitor""s high-frequency impedance. Furthermore, the self-resonance of discrete capacitors limits the useful bandwidth over which electrical disturbances can be attenuated. Moreover, because a discrete capacitor is necessarily mounted a certain distance away from the semiconductor chip, it is electrically coupled to the voltage pins by a plurality of power wiring lines or large power buses which typically represent high induction paths which add to the effective inductance of the electrical path. In addition, as the amount of current flowing in the plurality of wiring lines increases, a voltage drop is produced across the wires which adds additional power distribution noise.
Therefore there remains a need in this art for an improved capacitor structure for reducing electrical noise such as switching noise.
The present invention meets the foregoing needs by providing a multi-terminal capacitor structure that reduces the capacitor""s intrinsic series inductance by making use of a signal flow through arrangement. The preferred embodiment also provides a capacitor structure that can take advantage of flip chip circuit arrangements to reduce the extrinsic series inductance the capacitor could otherwise add to a circuit. The preferred capacitor structure also provides a mechanism whereby both the input impedance and the output impedance of the capacitor structure can be customized for better matching with power supply impedance and the associated interconnect impedance.
The present invention provides many advantages over the presently known capacitor structures. Not all of these advantages are simultaneously required to practice the invention as claimed, and the following list is merely illustrative of the types of benefits that may be provided, alone or in combination, by the present invention. These advantages include: (1) providing high-quality decoupling and electrical isolation of noisy power supply networks over a broad spectrum of frequencies thereby providing sub-component isolation; (2) the ability to customize both the input impedance and the output impedance of the capacitor structure thereby providing tuned terminations; (3) independent impedance looking into each pair of terminals; (4) avoidance of discrete capacitors leading to reduced system size; (5) application-specific optimization of sub-component isolation.
In accordance with one aspect of the present invention, a thin film capacitor structure is provided that comprises a first set of terminals and a second set of terminals. The first set of terminals comprises a positive input terminal and a negative input terminal. The second set of terminals comprises a positive output terminal and a negative output terminal. The capacitor structure further comprises a first electrode assembly coupled between the positive input terminal and the positive output terminal and a second electrode assembly coupled between the negative input terminal and the negative output terminal. Electrical energy available at the second set of terminals flows from the first set of terminals to the second set of terminals across said first and second electrode assemblies.
In accordance with another aspect of the present invention, a capacitive device formed on a substrate is provided that comprises a first set of terminals and a second set of terminals. The first set of terminals comprises a positive input terminal and a negative input terminal. The second set of terminals comprises a positive output terminal and a negative output terminal. The capacitor structure further comprises a first film electrode layer disposed above the substrate and having an input side and an output side, the input side having means for providing a coupling location for the negative input terminal, the output side having means for providing a coupling location for the negative output terminal. The capacitor structure further comprises a second film electrode layer also disposed above the substrate and having an input side and an output side, the input side having means for providing a coupling location for the positive input terminal, the output side having means for providing a coupling location for the positive output terminal. The capacitor structure also comprises a layer of film dielectric material disposed between the first film electrode layer and the second film electrode layer.